I purchased this game yesterday, never having played it before and I'm totally addicted. It has multiple levels ranging from character creation and RPG to Civ like city management. If Disciples, HOMM or Civ rock your boat this is a must have.
The 4X gaming has reached its current peak in Alpha Centauri. Though the diplomacy is still vague its far beyond what Civ games have ever offered. Otherwise the factions are a great addition, building your own troops and listening to the (real) philosophical comments on technologies deepens the mood of the game. Simply: One of the best games ever released.
Since other seem to be running the game nicely I was disappointed in noticing it bugs for me. The intro animation becomes laggy very quickly and the menus are bugging (they are black until you move mouse over them and the screen comes visible). Finally the game crashed when I tried to choose a mission and couldn't play it.